Fibre-cement products which may include board tiles and/or panels are commonly used in the building industry in the manufacture of sidings, exterior cladding, skirting and interior panels, and many other interior construction materials. In the industry, fibre-cement board may also be known as “fibreboard”.
The problem with fibre-cement products is that if water enters the product (eg a wall panel) before installation, the panel will expand slightly and, if installed, stress will build up in the panel as it dries that can lead to bowing and like problems. Thus it is clearly desirable that the fibre-cement product be water-resistant or water repelling to combat such problems.
The difficulty in producing water resistant fibre-cement products has been primarily due to the harsh conditions used during the preparation of the fibre-cement product. To increase its flexural strength, fibre-cement products are normally cured in an autoclave. The saturated steam pressure used is usually about 1000 KPa. The pressure is held at this level for approximately 8 hours, and the alkalinity of the board may be as high as a pH of 13. These harsh conditions affect the molecular integrity of the organic polymers used and this prevents the formation of water resistant fibre-cement.
Whilst many different hydrophobic polymers have been successful at waterproofing building materials, such as gypsum, they have failed to impart water resistance on fibre-cement products primarily due to the problems of the autoclaving process used for fibre-cement production:
In this specification, the relationship between a water repelling agent and fibre-cement is described by the term “integrally associated”. This term is understood to describe the substantially even spread or distribution of a water repelling agent throughout the fibre-cement.